The present invention relates to a system for selectably electrically pulsing each of a plurality of ultrasonic transducers in a non-destructive testing apparatus in rapid sequence. This system is well suited for use with testing apparatus, such as ultrasonic rail testing apparatus, that includes a plurality of transducers for producing a pattern of ultrasonic energy transmitted into and subsequently received back from the rail to thoroughly probe all portions thereof.
Various systems for ultrasonically inspecting test pieces are known. Such a system for inspecting a test piece, specifically a railroad rail, is disclosed in U.S. patent application Ser. No. 818,544, now U.S. Pat. No. 4,165,648, (Pagano) and includes leading and trailing ultrasonic inspection wheels adapted to roll on a railroad rail in spaced relation. An array of ultrasonic transducers is mounted in each inspection wheel and includes two transducers looking laterally of the rail, three transducers looking longitudinally, one transducer looking normally and one send/receive transducer. The send/receive transducer in the leading wheel operates in cooperation with the similar transducer in the trailing wheel to transmit ultrasonic energy thereto and receive ultrasonic energy therefrom in an alternating send/receive mode. Each of the transducers in the leading and trailng wheels is independently capable of transmitting ultrasonic energy, through a suitable coupling medium in the wheel, into the rail and of receiving ultrasonic energy transmitted back thereto to produce an individual response signal.
In order to operate such a rail testing apparatus at high speed to inspect the rail with a known recurring pattern of ultrasonic energy, it is necessary to be able to rapidly pulse the transducers in a known sequence chosen to minimize interference between the ultrasonic pulses generated by them as well as to rapidly recycle each transducer for subsequent pulsing.
In prior art ultrasonic testing apparatus employing a plurality of transducers, capacitors have been used to provide the pulsing power for each transducer. However, it has been found that when the transducers are rapidly pulsed in sequence, a voltage drop occurs across the capacitor or capacitors used to pulse the transducers, thereby limiting the rapidity with which the transducers may be recycled for driving.